The present invention generally relates to pointing devices, in particular for controlling the position of a cursor on a screen, such as the display of a personal computer, workstation or other computing devices having a graphic user interface. Such pointing devices may for instance include mice, trackballs and other computer peripherals for controlling the position of a cursor on a display screen.
The present invention more particularly relates to the field of optical pointing devices which comprise an optical sensing device including a photodetector array for measuring the varying intensity pattern of a portion of a surface which is illuminated with radiation and for extracting information about the relative motion between the photodetector array and the illuminated portion of the surface.
Optical pointing devices are already known in the art. U.S. Pat. No. 5,288,993, which is incorporated herein by reference, for instance discloses a cursor pointing device utilizing a photodetector array and an illuminated target ball having randomly distributed speckles. U.S. Pat. No. 5,703,356 (related to the above-mentioned U.S. Pat. No. 5,288,993), which is also incorporated herein by reference, further discloses (in reference to FIGS. 23A and 23B of this document) an optical cursor pointing device in the form of a mouse which does not require a ball and wherein light is reflected directly from the surface over which the pointing device is moved.
The imaging technique used in above-cited U.S. Pat. No. 5,288,993 and 5,703,356 in order to extract motion-related information is based on a so-called xe2x80x9cEdge Motion Detectionxe2x80x9d technique. This xe2x80x9cEdge Motion Detectionxe2x80x9d technique essentially consists in a determination of the movement of edges (i.e. a difference between the intensity of pairs of pixels) in the image detected by the photodetector array. Edges are defined as spatial intensity differences between two pixels of the photodetector array. The relative motion of each of these edges is tracked and measured so as to determine an overall displacement measurement which is representative of the relative movement between the photodetector array and the illuminated portion of the surface.
More particularly, according to U.S. Pat. No. 5,288,993, edges are determined between pairs of pixels aligned along a first axis of the photodetector array (for example in each row of the photodetector array) and between pairs of pixels aligned along a second axis of the photodetector array (for example in each column of the photodetector array). According to U.S. Pat. Nos. 5,288,993 and 5,703,356, the overall displacement measurement is evaluated based on a normalized difference between the number of edges which move in a first direction along the first axis and edges which move in the opposite direction along the first axis (for example edges which from left to right and right to left in each row of the photodetector array), and, on the other hand, based on a normalized difference between the number of edges which move in a first direction along the second axis and edges which move in the opposite direction along the second axis (for example edges which move downwards and upwards in each column of the photodetector array).
Relative motion of edges is determined by comparing the position of the edges in the photodetector array at a first point in time with the position of edges in the photodetector array at a subsequent point in time. The optical pointing device thus typically comprises a light source (such as an infrared LED) which intermittently illuminates the portion of the surface in accordance with a determined sequence, and the pixel outputs of the photodetector array are sampled in accordance with the determined sequence to provide two successive sets of edge data that are compared to each other in order to determine a relative motion measurement.
A problem of the above solutions, in particular with optical mice wherein radiation is reflected directly from the surface over which the pointing device is moved, resides in the fact that random surfaces (such as paper, wood, etc) have a lot of high spatial-frequency content. This high spatial-frequency content results in too much information (or noise) for the sensing device and a possible degradation of the quality and accuracy of the relative motion measurement extracted by the sensing device. In practice, the xe2x80x9cEdge Detection Techniquexe2x80x9d disclosed in the above U.S. Pat. Nos. 5,288,993 and 5,703,356 has been applied with success to trackball devices wherein radiation is reflected from a surface having specific patterns, in this case a ball having a plurality of randomly shaped markings thereon in a color which contrasts with the background. The dimensions and density of these markings on the ball surface are selected for optimal determination of the relative motion measurement.
Accordingly, it is an object of the present invention to provide a solution that is better suited for application to optical pointing devices where radiation is reflected from random surfaces.
It is another object of the present invention to provide a solution that remains of simple design and construction.
According to a first aspect of the invention, there is provided a sensing device for an optical pointing device comprising a plurality of pixels, each one of the pixels comprising a photosensitive element for generating a pixel output signal in response to radiation reflected from an illuminated portion of a surface, the sensing device further comprising processing means for determining, based on the pixel output signals, a measurement of relative motion between the sensing device and the illuminated portion of the surface and for generating cursor control signals based on this measurement,
wherein the sensing device further comprises circuit means for summing the pixel output signals of subsets of pixels including at least two pixels and for generating, for each of the subsets of pixels, a summed output signal,
the processing means determining the measurement of relative motion based on the summed output signals.
There is also provided an optical point device including the above sensing device.
According to a preferred aspect of the invention, the circuit means for summing the pixel output signals include a plurality of distinct summing circuit means each associated with a distinct subset of pixels. Preferably, at least a first and a second subset of pixels overlap each other and include at least one common pixel.
According to the present invention, processing of the data is performed based on the sum of several pixel output signals. Such summing has an averaging and filtering effect which reduces high frequency spatial signals and thereby reduces spatial-frequency aliasing.
Other aspects, features and advantages of the present invention will be apparent upon reading the following detailed description of non-limiting examples and embodiments made with reference to the accompanying drawings.